The present invention relates to a device for measuring the particulate content of gas, which may contain corrosive dusts from a stationary source, like a flue, as in a chimney, in which an equal velocity or isokinetic removal of a sample stream of gas takes place and the sample stream of gas is mixed with fresh air and is fed to an evaluation filter.
Embodiments of this type of device are disclosed in German Patents 20 32 127 and 22 37 736. Those embodiments, however, have several disadvantages. First, the throttles of the device become dirty very rapidly. Secondly, during operation, deposits form on the shafts of the pneumatic controllers, resulting in very expensive maintenance and down time of the measuring devices. Therefore, rubbish incineration plants, which must be operated with emissions measurement, must be shut down during maintenance. Furthermore, in known devices, there is a danger of the measurement diaphragms icing if the outside temperatures fluctuate around the freezing point. Due to maintenance requirements, the percentage of availability of these devices is less than 90%. Finally, the control response of these devices is sluggish.